Seismograph blasting cap



Feb. 6, 1940. J. P. MINTON SEISMOGRAPH BLASTING CAP Filed NOV. 17, 19372 Shets-Sheet 1 2 Cumi/vr AMPSllllllllllllllllllllllllllllllllllllllllllllllll I! 3mm 6in 24/122101;

MWEW

- Feb. 6, 1940.

J P. MINTON SEISMOGRAPH .BLASTING CAP 2 Sheets-Sheet 2 Filed NOV. 17,1937 WMQQKS Patented Feb. 6, 1940 John P. ltfinton, assignments,Incorporated, of New York Application November 17, 1937, Serial No.174,970

- 2 Claims. (Cl. 181-05) This invention relates generally to electricutilized. This is likely to be confusing to the blasting caps and moreparticularly to that type operator in properly connecting the cap to itsof blasting cap that is employed in seismographic circuits. Also, theexpense of a third conductor prospecting. is a consideration. The lattermethod described surface. By recording and observing the characother twobeing the signal circuit. Additionally teristics of the seismic wavesthus generated, it the use of this method requires that currents of ispossible .to ascertain physical characteristics substantial magnitude,flowing in the signal cirwaves, is detonated. charge can be forced tothe depth required. The In the past it has been customary, for the edgesof the casing at the assembly joints are usumost part, to record theelectrical impulses caused ally quite rough and there is ever presentthe by the fusing of'the detonating caps fuse. It has danger of scrapingthe insulation from the conbeen assumed. for purposeof computation, thatductors leading from the cap, or even in some ,this instant correspondsto the instant of detonacases of entirely severing or breaking theconduction of the dynamite. Due, however, to possible tor. For thisreason, it is always desirable to use posed to circumvent thisdifiiculty and to secure the time of detonation, which have been com- 30carried out a great deal of research and developseismogram.

5 ment to avoid the possibility of errors entering The principal objectof this invention is to into seismic computations caused by cap-lag andovercome the objectionable features of prior other varying factors. Atthe same time geomethods outlined above. This is accomplished, physicalcompanies have given much thought to according to this invention, byproviding an e1ecthis particular diiflculty. tric blasting cap for usein seismographic pros- For example, numerous methods and circuitspecting having dual bridges. For the purpose of have been designed forthe purpose of recording eliminating the time lag referred to above. asecattached thereto, two of which are used for-the fuse from the outputof the blasting generator purpose of detonating the cap, while thethird, used. Using a second bridge in this manner when ruptured by thebursting of the cap, is used causes the electric blasting circuit toremain unto give a signal to indicate the instant of detonadisturbeduntil the detonation of the blasting cap tion. Asecond method that hasbeen extensively ctua y s effected, and there can 110 time usedheretofore consists in the use of separate interval between theinstantof detonation of'the 5 conductor will be blown apart, thereby openingOwn -8 pencountered e using the be recorded to indicate the time ofdetonation. ing variations amongst the caps. I

Methods such as those described above are open Other objects andadvantages of this invention to objection. In the first case three leadsare will be apparent from the following detailed devcntlonal bridge inmany instances,

- clapses between the instant at wire fuses and that at which the capactually 'detonates.

'- stances where .error occurs, in some as from .01 to .02 of 3 capoccurs.

bridge 1 is selected so that the will flow through the bridge 4imscription when considered with ing drawings in which:

Figure 1 is a longitudinal section of an electric blasting cap that isillustrative of this invention.

Figure 2 is a curve which has been plotted with current as abscissa andtime as ordinates.

Figure 3 is a circuit diagram partly illustrated schematically showingthe relation between the electric blasting cap and the electricseismograph with which such a cap is to be used.

Referring to the drawings in detail, in Figure l the shell i, which maybe of copper-zinc alloy or any other suitable material, is usually firstloaded" with a base next placed on the accompanytop of the base charge.The conwire, as illustrated at 4, having the proper characteristics suchthat it will fuse to ignite the primer charge, is usually connectedacross the ends of the conductors 5 and 8, and. is embedded in theprimer charge. The detailed description thus far is that of aconventional electric blasting cap, and is all that is necessary todetonate a charge of' explosive, but it will be noted that there are noprovisions made whereby the instant of detonation can be detected orrecorded. The actual time of detonation of the cap as shown by Figure-2,is not always the same as the instant at which the fusing of the bridgewire 4 takes place. In many inthe detonating current flowin through thefusible bridge d of the cap is caused to build up relatively quickly, anappreciable time Therefore, it becomes apparent that if, as is commonpractice, bridge wire fuses and opens used as a signal to indicate onthe seismogram the instant at which detonation takes place, an unusualinstances as much a second. An error of this magnitude in seismographicwork creates a substantial error in depth computations, thereby reducingthe accuracy of the work. This difllculty is overcome according to thepresent invention .by placing a second bridge l, of higher resistancethan bridge d, across the conductors 6 and b as shown. This bridge wireI will not be ruptured to open the cap circuit until actual detonationof the The size and resistance of this second greater portion of thecurrent bedded in the primer charge and fuse it. The

position of the second bridge 1 relative to the first bridge 4 is notcritical so long as it is placed at a point where there will be no doubtof its being ruptured by the detonation of the cap. The use of thesecond bridge effectively prevents the elecfrom being broken until thecap actually detonates and blows the bridge apart. The opening of thecap circuit by breaking this second bridge causes the current to die outof the circuit abruptly in the form of a surge, and this surge orimpulse can be utilized as a signal to indicate the exact instantatwhich detonation occurred.

Although the above described electric blasting cap of this invention canbe employed to -produce a signal of the time of detonation of the chargeof explosive in a number of different electric seismograph circuits,there is shown in Figure 3 an electric seismograph circuit in which ithas been used successfully. In Figure 3 there is illustrated theconventional geophone il'con'nected to the in cate elapsed time charge2. Then a primer charge 3 is.

which the bridge blasting cap put of an amplifier l, the amplifier 9 inturn having its output terminals connected to a conventional recordinggalvanometer iii. In order to 11- lustrate a complete and operableelectric seismograph, there is indicated at i l a timer or means forgenerating a signal of definite frequency which can be recorded on thegalvanometer ill to indie during the recording period. There is alsoconnected to the galvanometer iii an electric blasting and signalcommunicating circuit. In this circuit there is illustrated an electricblasting cap l2 having dual bridges 4 and 1, the bridge wire shown at 4being the one which actually fuses to detonate the electric blasting capwhile that shown at 1 remains intact to complete the blasting circuituntil the detonation of the blasting cap ruptures it. When the bridge 1is ruptured by the detonation of the electric blast-' ing cap, a signalin the form of a transient voltage is thereby generated in the blastingcircuit and is communicated through the transformer T1, the conductorsY, to the time break and communication circuits H, in the recordingtruck and finally to the recording galvanometer Ill. This signal whenrecorded on a seismogram will mark the exact instant of detonation ofthe explosive. Thus it can be seen that the possibility of errorsentering into the overall time between the instant of detonation and theactual recording of seismic waves is positively eliminated.

I claim:

1. In an apparatus for seismic survey, includin a blasting circuit, asource of power for energizing the circuit, arecorder for recordingseismic waves and a communication circuit connecting the blastingcircuit with the recorder, an improved blasting structure comprising adetonating substance, a plurality of conductors extending into saidstructure, fusible means lying in contact with the detonating substanceand connected to the conductors, frangible electrical conducting meansdisposed within the structure and connected to the conductors tonormally maintain the blasting circuit closed, said frangible meansbeing so positioned with respect to the detonating substance that itwill be ruptured coincident with the detonation of the substance togenerate a transient voltage that will be communicated to the recorderas an indication of the exact instant of detonation of the explosivecharge.

2. In an apparatus for seismic survey, including a blasting circuit, asource of power for energizing the circuit, a recorder for recordingseismic waves and a communication circuit connecting the blastingcircuit with the recorder, an improved electric for the detonation ofexplosives to generate seismic waves comprising a shell, a detonatingsubstance within the shell, a pair of conductors extending from theblasting circuit to a point within the shell, fusible means connected tothe conductors and lying in contact with the detonating substance withinthe shell, for igniting the detonating substance, frangible conductingmeans connected to the conductors but disposed within the'shell adjacentthe fusible means and detonating substance in such a manner that thefrangible means will be ruptured on detonation of the detonatingsubstance to generate an electrical signal in the blaster circuit thatwill be communicated to the recorder as the indication of the instant ofdetonation of the electric blasting cap. 1

JOHN P. MINTON.

independent of the fusible means, I

